1. Field of the Invention
The present invention relates generally to a scheduling system and method in a communication system, and in particular, to a system and method for performing uplink scheduling in a communication system.
2. Description of the Related Art
Generally, the next generation communication system is evolving into an advanced system for providing high-speed, high-capacity data transmission/reception services to subscriber stations (SSs). A wireless broadband Internet communication system based on the Institute of Electrical and Electronics Engineers (IEEE) 802.16e standard is a typical example of the next generation communication system. In the wireless broadband Internet communication system, data transmission is performed on a frame by frame basis, and each frame is divided into a region for transmitting downlink data and a region for transmission uplink data. The region for transmitting the uplink data is formed in a 2-dimensional arrangement of (frequency domain×time domain), and each element of the 2-dimensional arrangement becomes a slot, which is an uplink resource allocation unit. That is, the frequency domain is divided in units of subchannels, each of which is a bundle of subcarriers, and the time domain is divided in units of a plurality of symbols, for example three symbols. Therefore, the slot represents a region where three symbols are occupied by one subchannel.
In addition, each slot is allocated to only one particular mobile station (MS) among the MSs located in one cell, and a set of slots allocated to the MSs located in the one cell becomes a burst. In this way, the wireless broadband Internet communication system allocates the uplink resources in such a manner that each MS uses the slots on a sharing basis.
In the uplink of the existing communication system such as a Code Division Multiple Access (CDMA) 2000 communication system and a Wideband Code Division Multiple Access (WCDMA) communication system, a signal transmitted from one particular MS serves as an interference component to another MS. Therefore, the existing communication system performs power control such that the signals transmitted by all MSs are received at a base station (BS) at almost the same received power regardless of channel states between the MSs and the BS.
In this case, however, the MS having a good channel state with the BS cannot use its full transmission power resources, causing inefficiency. In addition, the existing communication system enables a plurality of BSs to receive the signal transmitted by one MS, using soft handover or softer handover. As a result, it indicates that uplink scheduling should be achieved in a BS's upper layer rather than the BS. Therefore, in the uplink of the existing communication system, uplink scheduling is mainly performed on a circuit basis, using a data rate control scheme that increases or decreases a data rate of each of the MSs according to loading.
The uplink of the wireless broadband Internet communication system is different in characteristics from the uplink of the existing communication system. The differences in the characteristics are as follows.
First, the wireless broadband Internet communication system has a characteristic that when a BS receives a signal transmitted by a particular MS, the signals transmitted by other MSs in the same cell do not serve as interference to the received signal. This is because all MSs in the same cell perform a ranging operation to acquire synchronization so that the signals transmitted by different MSs should be simultaneously received at the BS, and use a Cyclic Prefix or Cyclic Postfix so that the signals received at the BS through multiple paths at different times do not serve as interference to each other.
In addition, due to the characteristic of Orthogonal Frequency Division Multiple Access (OFDMA) used by the wireless broadband Internet communication system, the subcarries used in the wireless broadband Internet communication system are orthogonal to each other. Therefore, in the wireless broadband Internet communication system, the signal transmitted by an MS through a particular slot does not affect the signals transmitted through other slots. This is equivalent in effect to allowing the downlink of the existing communication system to use different orthogonal codes so as to prevent the signals targeting MSs from serving as interference to each other.
Second, the uplink of the wireless broadband Internet communication system has a characteristic that it uses hard handover due to the characteristic of the diversity subchannel allocation scheme, neighbor BSs or neighbor sectors use different subcarrier permutations. The diversity subchannel allocation scheme, a scheme for mixing and grouping a plurality of subcarriers included in the full frequency band used in the wireless broadband Internet communication system in a different way for every BS (or sector), generates a plurality of diversity subchannels and allocates the generated diversity subchannels to a corresponding MS.
Due to the uplink characteristics of the wireless broadband Internet communication system, there is a need for a new uplink scheduling scheme different from the uplink scheduling scheme of the existing communication system.